The present invention relates to optical systems and, more particularly, to systems and methods for tracking wavelength communication channels through WDM (Wavelength Division Multiplexing) systems.
In WDM systems, multiple optical signals having different wavelengths share an optical fiber, each wavelength defining a particular communication channel. WDM systems have many advantages in implementing optical communications including increased capacity and the ability to use passive optical components to redirect all, or a portion, of the data flowing along a fiber. In a stricter sense, WDM refers to an ITU (International Telecommunications Union) standard that includes the specification of the particular channel wavelengths and the spacing between these channels. DWDM (Dense WDM) refers to a more recent ITU standard in which the channel spacing is tighter with more wavelength channels packed into an optical fiber. The term WDM as used herein refers to the first, more inclusive sense such that is includes both the ITU WDM and DWDM standards, unless specifically stated otherwise.
When transmitting optical signal from a source to a destination, the endpoints of the connections are established and known. However, in large networks, such as a global telecommunication network, there are many possible paths or routes exist that will deliver the data from the source to the destination. In any telecommunication network, it is critical to managing the network to track the route through the network for each connection.
Tracking occurs in the physical domain without reliance upon data maintained by the network system management or by node software. Because of the critical role that route tracking plays in maintaining the reliability of the telecommunication network, tracking must be immune to configuration errors, software failures, as well as hardware (switch) failures.
Typically, information in a frame header contains an identification sequence unique for each node in a communication route that each node along the route appends to the frame header. To identify the route, it is only necessary to extract the identification sequence. However, in WDM networks, the inability of the WDM hardware to look into the frame encoded in the wavelengths exacerbates the problem of route tracking because the header information is unavailable. Thus, while route tracking identification inside SONET/SDH or G.709 frames may suffice to detect a source-to-destination misconnection, it is not sufficient to find the route through the interior of the network.
One traditional way to implement route tracking in WDM networks is to use a fast pilot tone mechanism, the mechanism and operation of which are well known in the art. However, such a mechanism requires dedicated hardware for the generation and the diction of the tone. With a relatively fast modulation of the carrier signal, i.e., at a frequency low enough to avoid disturbing the signal data rate (currently 1 Gbps and higher) but high enough to pass through the automatic power control loops in the amplifier and other network equipment, a route can be tracked through a WDM network. Unfortunately, pilot tones require specialized and expensive hardware for generating, as well as detecting, through the network. It is also very difficult to add such hardware to existing WDM networks deployed without such specialized hardware. Another disadvantage that arises with the use of pilot tones is the degradation of the optical signal and the introduction of jitter.
What is needed is a mechanism for tracking wavelengths in a DWDM network without specialized hardware. An inexpensive and flexible mechanism that has maximum optical performance with functional flexibility is preferred.